[Speed] External sources of noise changing call_simple "performance"

[Victor Stinner]

2016-05-18 8:55 GMT+02:00 Maciej Fijalkowski <fijall at gmail.com>:
> I think you misunderstand how caches work. The way caches work depends
> on the addresses of memory (their value) which even with ASLR disabled
> can differ between runs. Then you either do or don't have cache
> collisions.

Ok. I'm not sure yet that it's feasible to get exactly the same memory
addresses for "hot" objects allocated by Python between two versions
of the code (especially when testing a small patch). Not only the
addresses look to depend on external parameters, but the patch can
also adds or avoids some memory allocations.

The concrete problem is that the benchmark depends on such low-level
CPU feature and the perf.py doesn't ignore minor delta in performance,
no?

Victor